Exercises aimed at strengthening the abdominal muscles include the traditional sit-up and legs-up movements. This type of movement, typically performed lying supine on a flat surface of the floor causes negative stress to the spine and can lead to back muscle and spinal injuries. Because of the flat surface, the starting position tilts the pelvis and tends to straighten the natural curvature of the lumbar section of the spine. When performing a sit-up or legs-up movement in this position, injuries such as back muscle strain, particularly the lumbar muscles, or abnormal compression of intervertebral discs leading to slipped or herniated discs and pinched nerves may occur.
The ordinary sit-up movement is initiated in the neck area, specifically by the contraction of the neck muscles, followed by the pectoral muscles and finally the abdominal muscles. This progression of muscle groups produces negative stress along the length of the spine tending to straighten it first in the cervical section, then in the thoracic section, and finally in the lumbar section. Because the lumbar section of the spine is unsupported by the flat floor, the ordinary legs-up movement produces the same compressive pressures on the vertebral column as the sit-up movement.
FIG. 9 illustrates the negative stresses on the spine and the tendency to straighten the spine during an ordinary sit-up movement performed on a flat surface. The first 15° of the movement are initiated by the neck muscles attending to the 100% pull of the head. During this fraction of time, the spine bears 85% of the stress produced by the weight of the head because the abdominal muscles do not begin to contract until after the second half of the movement, or until the torso has moved past 45°. From zero to 45° the spine is under tremendous stress which tends to straighten the natural curvature of the spine and it is most apparent when observing exercisers in action. The head, at that initial moment is much heavier due to gravitational acceleration. Additionally, the drastic and sudden initial effort of lifting the head can compare to a car whiplash, with all the complications that this condition may comport to the cervical vertebral region.
The ideal abdominal exercise will reverse the order of muscle group engagement and prevent the negative stresses on the spine by maintaining the spine's natural curvature. Additionally, it is advantageous to simultaneously decompress or fully extend the lumbar section of the spine while stretching the abdominal muscles immediately before each sit-up movement. Full extension of the spine is not achieved when the back is flat on the floor, but rather when the spine is arched back or extended, a position the flat floor does not allow. Decompressing the spine helps to restore proper intervertebral space and allows the discs between the vertebrae to reacquire their proper thickness and function as the spine's shock absorbers. This exercising of the spine enhances the elasticity of cartilage and ligaments for a more flexible spine as well as enhances vertebral alignment and proper curvature of the spine. Further, the ideal abdominal exercise in addition to neutralizing the lumbar muscles should provide a starting position where the pelvis is not abnormally tilted and the torso or legs are free to pivot at the hip joint.
Numerous abdominal exercisers are known in the art. However, the prior art does not provide an abdominal exerciser that prevents negative stresses on the spine throughout a sit-up movement while additionally decompressing the lumbar section of the spine.
U.S. Pat. No. 4,372,553 to Hatfield discloses an exercising device having a seat in which the user sits and bends forward working against weights supported on a pulley system. The weights are connected to the user via a shoulder harness. The user's lumbar section is never fully extended throughout the movement and negative pressures are placed on the spine as the movement forces a progression of muscle groups instead of a simultaneous contraction.
U.S. Pat. No. 5,110,122 to Moore, et al. discloses an exercising apparatus that enables a large number of movements to be performed thereon especially abdominal and lower back exercises. The apparatus is generally a sectioned bench that comprises a seat supporting section, a back supporting section, and a head supporting section all initially in the same plane. Although the back supporting section may be inclined, it does not include an arched support to fully extend the vertebral column and performing a sit-up movement on the apparatus is identical to performing the movement on the flat floor.
U.S. Pat. No. 4,474,370 to Oman discloses a weight lifter's bench that includes a longitudinally adjustable pad providing lumbar support. The apparatus enables the user to perform the bench press exercise while supporting the cervical and lumber sections of the spine. While the apparatus is designed to support the lumbar region of the spine while developing body musculature, primarily the pectoral muscles of the chest, it does not exercise the abdominal muscles.
U.S. Pat. No. 4,953,857 to Lemire discloses an orthopedic back support attachment for a weight lifter's bench. The apparatus includes a padded cervical rest and a padded lumbar rest in combination with a padded mat each having a centrally aligned spine protecting channel that supports the back and eliminates the compression of the spinal column normally associated with weight lifting. The padded mat removably attaches to the top surface of a typical weight lifter's bench and the other two particularly shaped pads are removably attached to the pad side surface of the mat by the use of straps. Both the cervical rest and the lumbar rest are longitudinally adjustable to accommodate different size users. After attaching the padded mat to a bench, the bench loses its incline functionality. Additionally, the weight lifter's bench is not conducive to sit-up or legs-up movements.
U.S. Pat. No. 6,467,841 to Henschel, et al. discloses a longitudinally and height adjustable lumbar support attachment for a weight lifter's bench. The lumbar support is comprised of a plurality of interlocking stackable platelets. The platelets are relatively thin rectangular shaped members and the number of platelets used determines the height of the support. The removable lumbar support can also be used on the floor. In addition to the faults of the previously discussed weight lifter's benches, the rectangular shape of the support does not fully extend the lumbar section and thus does not decompress the spine.